February 26, 2011

Check out this animation by DAMOCLES on the greenhouse gas effect and the factors that influence it. The graphic below describes not only how the concentration of carbon dioxide in the atmosphere can change, but how the importance of a convecting mantle on the density and composition of the atmosphere on Earth suggests the questionable possibility for life on a planet without it.

This chart graphs how a planet's mantle activity or inactivity can impact the atmosphere.

February 22, 2011

Areios’ bulkier shape contains a more massive mantle hidden by a fragile lithosphere. Because Areios has such a thick mantle and a comparatively thin crust, there is more volcanism on the planet because magma from beneath the surface has a thinner crust to penetrate before it reaches the surface as lava. The tectonic cycle that builds and destroys land on Areios would operate in fast-forward; with portions of the crust being created and destroyed just as quickly, weathering would deplete carbon dioxide in the atmosphere and prevent a greenhouse blanket from keeping the planet warm enough to have liquid water on the surface. Also, increased volcanism would hurl sulfur dioxide out into the air, forming clouds that would reflect light back out into space. This would cool the planet down even more were it not for the water vapor spewed from eruptions and the dark colored basaltic rocks covering the planet to absorb incoming solar radiation. And as time goes by, Hemera would get brighter as it spends more of its fuel. Once life takes a foothold on Areios, methane-producing bacteria warm the planet up drastically in a climatic event akin to the Great Oxygenation Event of the Cambrian Era. But until then, the planet is frigid except in select spots where hydrothermal vents and hotspots keep it warm.

The atmosphere on Areios is regulated by this tectonic cycle that creates and destroys crust. Carbon dioxide produced by volcanoes would get scrubbed out of the atmosphere by the subduction of crust into the mantle. Because this process happens so much quicker on Areios, carbon dioxide would get scrubbed out of the atmosphere quicker than the processes operating on Earth. Areios’s mass keeps lighter gases like hydrogen from escaping so easily and this thicker envelope of gas around the planet means that carbon dioxide and other gases are available in higher concentrations than on Earth. So while carbon dioxide would get removed from the atmosphere by a hyperactive tectonic system and unceasing weathering, it would get replenished about as quickly by volcanoes and other natural processes. Clouds formed in the atmosphere can reflect heat if they form high in the atmosphere or they can absorb heat if they are lower in the atmosphere. Venus has clouds of water vapor and sulfuric acid, which would reflect light from the surface of the planet, but because it receives more incoming solar radiation than Earth and because its atmosphere is rich in the greenhouse gas carbon dioxide, what infrared radiation that does get in sticks around for much longer and heats up the surface of the planet enough to boil the carbon dioxide trapped in the carbonate-bearing rocks in the crust, heating up the planet more so. We’ll see how the chemistry in the crust can impact the composition of the atmosphere with an in-depth discussion of the plate tectonic system on Earth. When life arises on the planet, it too will manipulate the composition of the planet’s atmosphere; bacteria would convert carbon dioxide and hydrogen gas into methane, warming up the planet. As Hemera’s luminosity increases, photosynthesis can be achieved on Areios by a creature that develops a chloroplast to harness the light shining through Areios’ hazy atmosphere, one day creating oxygen for animal life.

Earth's atmosphere can reflect or absorb solar radiation.

With volcanoes spewing out hydrogen sulfide, water vapor and sulfur dioxide, radiation coming in from Hemera would disassociate the atoms of those molecules and form sulfuric acid in the atmosphere. Sulfuric acid would block some of the radiation from coming in, but on a planet as cold as Areios, the sulfuric acid in the sky would precipitate out and rain down on the surface, causing weathering to speed up as acid wears down the crust. Because of the thicker atmosphere on Areios caused by a greater gravitational pull from Areios’ larger mass, the partial pressure of carbon dioxide in the atmosphere would mean carbon dioxide gets incorporated into the crust more readily. This would cause carbonate rocks to neutralize the acid, creating bicarbonate in the crust. While Areios has less aluminum in the crust compared to Earth, acid rain would cause toxic metal leaching in the oceans. Water vapor and other gases with a higher freezing point would freeze into a solid on the surface and raise the albedo of the planet. Albedo is a measure of reflectivity, so raising the albedo would mean more light is being reflected back into space rather than being absorbed by the planet. This is especially disastrous for life when the planet gets cold enough to freeze carbon dioxide. Carbon dioxide is a greenhouse gas, but if it gets cold enough, it will bypass the liquid phase and sublime into a solid ice. As an ice, it would no longer trap heat and instead it would reflect it back out into space, making the planet even colder in a negative temperature feedback loop.

February 15, 2011

The Earth’s rotation has a profound impact on the environment. The friction of the moon’s orbit has been slowing down the rotation of the Earth very slowly over the last four billion years, and this has had a mediating effect on the velocity of atmospheric currents. Not only does the speed of our rotation influence the severity of our weather, but for Areios, the three small moons have less of a drag on the planet’s rotation, so Areios would rotate faster than Earth and has more intense weather patterns associated with a more vigorously churning atmosphere. The Coriolis Effect deflects the motion of our atmospheric currents, causing air currents to deflect towards the east in the Northern hemisphere and to the west in the southern hemisphere. While wind is generated by heating, it’s the Coriolis Effect that creates the prevailing winds we see at different latitudes. The weather on Areios has a more pronounced Coriolis Effect and because Areios rotates in a clockwise direction when seen from above (while the Earth rotates in a counter-clockwise direction), Areios would see winds deflected to the left in the Northern hemisphere instead of to the right like on Earth. Areios has a 256-day year as it revolves around Hemera and a 16 hour day that whips the atmosphere around creating monstrous storms over the planet. Most importantly, this vigorous atmosphere mixes the air currents so that the temperature on the planet is averaged out a bit more. Especially because Areios rotates on its side, the heat distribution around the planet can be at either extreme during winter and summer, where one side of planet is in darkness for weeks on end and the other side is scorched in perpetual sunlight for weeks on end. This would create a tremendous amount of evaporation, fueling intense hurricane activity where one side of the planet is experiencing summer.

During the summer months, Areios is at aphelion with Hemera, meaning that the planet is at its farthest approach from the star and during the winter months, the planet is at perihelion, or its closest approach to Hemera. The planet’s tilt determines the weather most significantly. The Earth’s atmosphere is made up of five distinct layers, much like on Areios. The layer of the atmosphere closest to the surface is called troposphere; this is where most of the atmosphere is contained and where all life and weather takes place within. As the altitude increases, we reach a point where the troposphere’s composition changes and makes way for the stratosphere. The stratosphere is where our ozone layer is located, which is important for keeping UV radiation from leaking into our atmosphere and causing higher incidents of cancer. Above the stratosphere is the mesosphere, where most asteroids will burn up upon reentry. And the outermost layer of the thermosphere contains the ionosphere where radio waves arriving from the surface get bounced off ionized particles in this layer and reverberated back down to Earth. Now beyond this ionosphere is the exosphere where the earth’s gravity effective gives away to outer space and the atmosphere stops. Unlike early Areios, the Earth has a magnetosphere that traps dangerous particles put off by the Sun; the magnetic field is generated by the rotation of the planet’s inner and outer core, which is influenced by the presence of our Sun, and its own magnetism and spinning core. Areios does not have this phenomenon at first because its hotter interior doesn’t form two distinct layers in the core until billions of years after its formation. Once the interior cools though, disparate motions of two distinct layers in the core will produce a magnetic field for Areios, which will help to prevent Hemera’s radiation from stripping away the atmosphere and bombarding the surface of the planet with ionized particles.

The early Areiosan troposphere is thick with smog; frequent lightning brought on by vigorous storms whip the atmosphere into a soup of chemicals that blocks out some of Hemera’s already dim light. While high levels of sulfur dioxide scatter the incoming solar radiation, carbon dioxide and water vapor spewed from volcanic eruptions trap what little heat is created and keep the oceans from frosting over. Areios’ greater mass means that it will retain lighter gases like hydrogen and helium, which escaped the Earth’s atmosphere early in the planet’s formation. This hydrogen becomes an important foodstuff for early life and contributes to the reducing environment of early Areios that makes the planet viable for the creation of life. As Hemera ages, it will warm up the cold planet, but until then, the atmosphere’s greenhouse effect suffices to keep Areios from becoming an ice world. The stratosphere is the most distinctly different; with no ozone layer to protect Areiosan life from UV radiation, the surface of the planet is still a dangerous place even with a hazy atmosphere obscuring light. The first life on Areios lives in the ocean before photosynthesis produces the oxygen that will make an ozone layer.

February 12, 2011

February 8, 2011

In our solar system, the Moon is the most massive satellite in the solar system relative to the size of the planet that it orbits. Because the Moon is so big compared to other satellites, its gravity tugs our oceans into areas of high and low tides, depending on the interactions of the Sun, the Moon and the Earth. Areios has three small moons, which makes their interaction with life on the planet interesting. We experience areas of high tide to the side facing the moon, and when the moon is at its farthest approach, we experience areas of low tide. If we didn’t have a moon, the Sun’s gravity on Earth would still cause some tides to occur, but not nearly as pronounced. Not only does the moon interact with the Earth’s oceans, the moon’s orbit has been slowing down the rotation of the Earth. The moon’s orbit has been growing wider and wider, too. In the next few billion years, the moon will fall into a closer orbit around the earth and get torn apart by the Earth’s gravity.

Our planet Areios has three moons, two of which were created from an impact event similar to the one that created Earth’s moon. The middle moon was an asteroid captured during the Late Heavy Bombardment era. Of Areios’ three moons, the innermost and outermost moons will wander out of Areios’ gravitational pull one day, but the middle moon will collide with the planet’s Roche Limit at some point, forming a ring of debris that could get dislodged and rain fragments down down Areios, spelling doom for anything unfortunate enough to be caught in the crossfire down below. Earth’s moon stabilizes the earth orbit, keeping the axial tilt of the planet in check, unlike Mars. Because Mars has two smaller moons, its axial tilt is out of control and the climate fluctuates wildly with each season without a massive moon to keep it in check. Areios experiences seasonal fluctuations more akin to Mars than Earth because its three moons all orbit with a different period and angle, only coming into alignment once every few hundred years. This would cause wild changes in weather leading to bitterly cold era of winter and longer blazing hot era of summer. These mood swings in climate could be challenging for any life on the planet to adjust to and such an unpredictable climate might lead to a higher rate of extinction during some epochs, and this would free up niches in the environment for new evolutionary forms to exploit, essentially increasing the turnover rate for species, so to speak.

On Earth, Milankovitch cycles caused by interactions with the gravitational fields of the other astronomical objects in the solar system with the Earth triggers regular perturbations in the Earth’s orbit, but these mild events happen like clockwork that a Serbian astronomer deduced their recurrence. Precession is any change in rotational axis or orbital path of a planet and both the Earth and Areios go through regular patterns of precession over geologic time. The Earth’s axis completes one full cycle of precession the orientation of Earth’s axis of rotation shifts slightly approximately every 26,000 years, creating a wobbling effect like a spinning top. At the same time the elliptical orbit rotates more slowly because of Jupiter or Saturn‘s gravity tugging at the Earth‘s orbit. The combined effect of the two precessions leads to a 21,000-year period between the seasons and the orbit. The angle between the Earth’s rotational axis and a perpendicular plane is call obliquity (or axial tilt), and the Earth moves from 22.1 degrees to 24.5 degrees and back again on a 41,000-year cycle. Areios goes through similar orbital changes but the most pronounced processional change is the obliquity in its rotational axis. Its axial tilt will vary up to a couple degrees every 35,000 years or so. Because the axial tilt is so extreme, Areios would experience different seasons and more extreme changes in weather.

Areios is very peculiar in that it rotates on its axis like Uranus, with the poles tilted very nearly onto the plane of revolution it has around Hemera. This gives it polar ice caps around the East and West instead of North and South. This strange arrangement was brought up briefly in the discussion of precession, but the impact that formed Areios’ two moons are also responsible for its off-kilter tilt of about 90 degrees. That means that the northern hemisphere is in constant light for weeks or months on end at one point and the other one is in constant darkness. Half an orbit later the roles are reversed. And halfway between those times, the rotational axis is perpendicular to the Sun’s direction, making day and night alternate in a way similar to what the Earth experiences at equinox. Any organism living on the planet would have to adapt with wildly-dramatic seasons that would vary from frigid temperatures in the winter to sweltering temperatures in the summers. Some creatures might adapt by burrowing into the ground to avoid the climate extremes and some may go into hibernation. We’ll discuss how animals survive such a harsh environment, but for now it will suffice to say that because these creatures have to live in an environment far different from what we find on Earth, a whole new set of morphological adaptations would be present on Areios to help them survive a solid month of perpetual sunlight or darkness.

February 6, 2011

Kepler finds 54 new planets that orbit in their stars’ respective habitable zone. For more information on the search for habitable planets, check out this link to NASA’s Ames Research Center on the Kepler mission.

February 1, 2011

Alkyoneus would dominate the Areiosan night sky as one of the brightest objects visible to the naked eye. This is because Alkyoneus is a planet more massive than Jupiter and its girth carries a strong gravitational field causing perturbations or disruptions in the orbits of its neighboring worlds. This gas giant can act as a shield, diverting dangerous comets and asteroids away from Areios, or the massive planet’s gravity can act as a plow, pushing the rocky debris left from the solar system’s formation onto a collision course with the planet through planetary migration. Areios’ water, for instance, came in part from planetoids left over from the accretion stage of Areios’ formation. Rocky chunks of planet collided and the heat from friction melted those bits together, forming ever bigger planetesimals that lead to full-fledged planets. Alkyoneus was such a big planet that its gravity would keep hold of gases swirling around and it enveloped so much mass that the atmosphere keep building until it was a gas giant planet. Gas giants like Jupiter or Alkyoneus have a mostly-silicate core and layers of gas thousands of kilometers thick that girdle the planet. The composition of Alkyoneus and its atmosphere reflects how close it was to Hemera when it formed. The current theory for the formation of our solar system is explained in the nebular hypothesis; the solar system started out as a swirling ball of gas with a dim star still forming and sucking in mass at the center. As particle grains grew by colliding with each other in a process called accretion, the velocity and direction that these particles were whipping around in became more or less averaged out, so all of the material flattened out into a disk with everything basically moving about on the same plane, in the same direction, at roughly the same speed. A few collisions might redirect the path of individual moons or planets, but eventually most of the matter in the solar system would get incorporated into a planet. The exception to this in our solar system has to do with Jupiter’s gravity; its mighty pull tore apart anything orbiting around where a fifth terrestrial planet could be expected and kept it from forming anything bigger than the asteroid Ceres. In Areios’ solar system, there are a significant number of asteroids in a belt between Areios and Alkyoneus, representing a mass about equal to Earth’s moon.

The asteroids in Earth’s solar system are categorized by their composition. C-type asteroids are carbaceous (carbon-rich) and s-type asteroids are silicatious (silicate-rich), with more c-type asteroids farther from earth and s-type asteroids closer to us. Planets that form close to the star would have much less volatile content; volatiles are things like water or carbon dioxide that would boil away early on in the planet’s formation from the heat given off by its star. Hemera may be dimmer than our Sun, but anything caught too close to its radiation would melt. This is why terrestrial planets are found closer to the Sun in our solar system than the gas giants; as the solar system formed, the Sun wasn’t a fully-functional main sequence star and the composition of the nebula swirling around it was homogeneous. So as the Sun condensed and started to heat up, it melted the frozen ices closest to the Sun, leaving behind silicates and metals, which have a higher boiling point than ice. A star’s luminosity decreases with distance, so the radiation that reaches the middle to outer portions of the solar system wouldn’t melt the ices as much, so ices and volatile chemicals would make up a greater proportion of the planets farther out.

Once the planets formed, Alkyoneus’ gravity started to hold on to more gas vented from the crust or sucked in from the nebula surrounding the planet and the weight of the atmosphere crushed any hydrogen gas closer to the core into a metallic form. On the periodic table hydrogen is above lithium and the alkali metals, suggesting that because they’re in the same period, they would have similar properties. Hydrogen only behaves like a metal under the most extreme pressures, but when it’s condensed into a metallic form, the hydrogen nuclei form a tightly packed grid and the electrons are no longer confined to any individual proton, like in a sea of electrons. From the metallic hydrogen core, Alkyoneus’ atmosphere has bands of cold dense gases and other streams of hotter and faster moving gases. Alkyoneus’ atmosphere is made up of hydrogen, helium, and traces of methane, ammonia, cyanide, carbon monoxide and noble gases. There is more than enough organic material to start life, but there are concerns about buoyancy; any life has to stay in a layer of the atmosphere that’s not too hot or too cold, so altitude within the clouds has to be carefully maintained because if a creature rises too high or sinks too low, they could freeze, broil, or be torn apart by fierce winds. To maintain the right depth, a creature would need an organ like an air bladder (akin to the swim bladder on a fish that keeps it from sinking or floating to the top of the water), but primitive life couldn’t have a complex feature like this, so if a single-celled organism can’t have a swim bladder, it’s hard to imagine a complex creature ever being able to evolve.

A depiction of the gas giant Alkyoneus and its seven moons, the Alkyonides